The present invention relates to a unit for controlling the shaft for selection and engagement of the gears of a gear change.
In particular, the present invention relates to a unit for controlling the shaft for selection and engagement of the gears of a gear change of the mechanical type in the shape of an xe2x80x9cHxe2x80x9d, with selection of the gears by means of axial displacements and engagement of the gears by means of angular displacements, and which is suitable in particular for being fitted onto vehicles which have transverse transmission.
As is known, gear changes which are currently in use for vehicles comprise a gear box, from which there projects at least one shaft for selection and engagement of the gears, by means of which the driver of the vehicle can select and engage the required gear. In the most common gear changes, the gears are selected and engaged by making the shaft for selection and engagement of the gears undergo a combination of rotations and axial displacements, which define gear changes of the mechanical type in the shape of an xe2x80x9cHxe2x80x9d. With reference to FIG. 1, the positions of engagement of the gears are in fact disposed according to a configuration in the shape of a double xe2x80x9cHxe2x80x9d, in which the gears are subdivided into groups of two (for example 1-2, 3-4 and 5-R), which are commonly known as xe2x80x9ccrowsxe2x80x9d, such that, from a reference position which is normally located in the centre of the double xe2x80x9cHxe2x80x9d, the xe2x80x9crowxe2x80x9d is selected by means of axial displacement of the shaft for selection and engagement itself, and the gears are engaged by means of angular displacement of the shaft for selection and engagement itself.
The devices which are currently in use for controlling the shaft for selection and engagement substantially comprise a control shaft which can be connected to the shaft for selection and engagement of the gears of the gear change, and a pair of actuators, which are connected to the control shaft, such as to be able to rotate the latter and displace it axially.
In particular, if the row is selected by means of axial displacements of the shaft for selection and engagement of the gears, the linear actuator which controls the axial displacement of the control shaft can make the control shaft assume three different axial positions (four in the case of a gear change with six gears plus reverse), to each of which there corresponds selection of a row, whereas the actuator which controls the angular displacement of the control shaft can make the control shaft assume three different angular positions, to each of which there corresponds engagement of a gear or the neutral position.
The said actuators are normally actuated pneumatically, hydraulically or electrically, and are controlled by an electronic control system.
Control units with two linear actuators have the major disadvantage that they required relatively complex components, such as hydraulic actuators which have several positions, valves, units for regulation of the paths, and position transducers, which increase the production cost of the unit. In particular, since linear actuators with several positions, which displace the control shaft axially in order to implement selection of the rows, need to be very accurate in positioning the control shaft, this requires mechanical processing and technical solutions which are highly specialised, which make the unit particularly expensive to produce.
The object of the present invention is thus to provide a unit for controlling the shaft for selection and engagement of the gears, which is more economical and simple to produce than those which are known at present.
According to the present invention, a unit is provided for controlling the shaft for selection and engagement of the gears of a gear change, wherein the shaft for selection and engagement of the gears is mobile, after axial displacements and/or rotations have taken place, between a plurality of gear engagement positions, to each of which there corresponds engagement of a gear or of the neutral position; the positions of engagement of the gear being disposed according to a selection grid in the shape of an xe2x80x9cHxe2x80x9d in which the gears are distributed in rows of two; the control unit comprising:
an outer housing;
a control unit which is fitted on the said housing, such as to be able to rotate angularly around its own axis, in order to implement a manoeuvre of engagement/release of the gears, and is axially mobile along its own axis, in order to implement a manoeuvre of selection of the row of gears; for each row of gears the said control shaft also being able to assume three different angular positions, corresponding respectively to a neutral angular position and two angular positions for engagement of the gear;
movement means, which are designed to displace the said control shaft angularly around its own longitudinal axis, between the said three different angular positions; and
cam guide means, which are connected mechanically to the said control shaft, and which, during the angular displacement of the control shaft which implements the passage between the two angular positions of engagement of gears in a row, are designed to impart selectively to the control shaft itself axial displacement which is sufficient to implement the passage to the row which is immediately adjacent, such as to implement the passage between consecutive gears which belong to consecutive rows;
the control means being characterised in that the said cam guide means are axially mobile along the control shaft, between a plurality of row-change positions, at each of which it can guide the control shaft in the said combined angular and axial displacement, which is sufficient to transform the passage of gear between two gears which belong to a single row, into a passage of gear between two consecutive gears which belong to two consecutive rows.